Gareth Ross, PhD’s work at Aston University’s Biomaterials Research Unit (UK) focuses on surface properties and solution interactions of contact lenses and multipurpose solutions.
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Gareth M Ross, PhD, Val J Franklin, PhD, Brian J Tighe, Biomaterials Research Unit CEAC Aston University, Birmingham, UK
Purpose: With multipurpose solutions moving further away from simple surfactant cleaners with successive developments, there is a need to measure and predict the role of combined components such as surfactants/polymers/biocides in the removal of proteins and lipids.
Method: A range of in vitro techniques have been developed that establish the link between cleaning and physical properties. They include dynamic (DST), static surface tension (ST) and the in vitro spoliation of lenses with a tear model solution containing both proteins and lipids in combination with fluorescence and UV spectroscopy. This allows the cleaning efficacy of solutions to be compared.
Results: The static surface tension results show that the commercial multipurpose solutions have ST between 30-40. However, the dynamic surface tensions show not only different values for different solutions but also the way the DST changes with surface age, with solutions with the same surfactant showing measurable variations. In vitro cleaning efficacy testing shows that even if the same surfactant is used the other components present effect the cleaning efficacy. Distilled water gives a relative cleaning efficiency of 20-30% removal whereas the most effective commercial lens products produce values around 80% removal of the deposited tear components. The efficacies vary for individual proteins and lipids dependent on the lens material and deposition profile.
Conclusions: The cleaning efficacy of multipurpose solutions can be linked to the individual components included. The surfactant is the dominant force but the other solution components influence and modify the behavior of the surfactant alone and this in turn affects cleaning efficacy